1. Field of the Invention
The present invention relates to a remotely operated vehicles and more specifically to computer enhanced environment visualization of a remotely operated vehicle.
2. Description of Related Art
Typically there is a need for inspection of machines or structures which are in environments which are inaccessible or very hazardous for humans. Several such environments would be inside a nuclear reactor boiler, deep beneath the sea, in a forest fire, in an oil well or in an area contaminated with a poisonous gas. The high temperatures, radiation exposure, high pressure, or toxic effects of these environments are clearly dangerous for humans. The space requirements to examine an in-line pump within an oil well or other environments with limited space also preclude humans access.
Typically these machines and structures within these environments have been inspected or repaired by remotely operated vehicles (ROV). These ROVs may be attached to a control unit some distance away by a tether cord or may be run by radio signals from a control unit at a safe distance away. The ROVs typically have a method of sensing their environment, with a testing or imaging device, such as a video camera. ROVs also employ a means of propelling themselves around their environment. In a fluid, like water, it may be a number of propellers driven by electric motors.
The use of ROVs also typically require a method of determining the position and orientation of the ROV (and/or its subparts) with respect to the operating environment allowing it to successfully move the ROV through the inspection environment. An example of a position sensing system employs SONAR operating through the water of the nuclear reactor boiler. Conventional systems require complicated compensation schemes and frequent recalibration to offset the errors due to variations or noise in the environment. For example, the time of flight of a SONAR signal depends on the temperature of the water through which the SONAR pulse travels. Temperature gradients within the pressure vessel must be carefully mapped and monitored to allow accurate position determination.
Typically the ROV will carry a number of inspection sensors. Typical sensors include underwater TV cameras, ultrasound flaw detection transducers, thermal imagers and point probes, such as microphones.
The major problem in the use of ROVs for inspection and repair in these remote environments is the difficulty of accurately positioning the ROV at desired locations within a complicated environment and then verifying that position and orientation, and passing the position and orientation to persons analyzing data from the ROV or other support personnel.
Another problem occurs as the ROV is moved from one site to another manually within the environment. In this situation, it is difficult to accurately determine the ROV's position at a given instant. Since one of the sensors typically carried is an underwater TV camera, the operator will often try to use the video from the camera to determine the exact position and orientation of the ROV, especially when the camera is not facing in the direction the ROV is moving. Typically the operator will zoom the camera back to wide angle and may move the ROV further away from a particular feature in an attempt to determine where in the environment he actually is. This task is made easier to the extent the position and orientation sensing system is accurate and reliable. Often, the P&A systems are not very accurate and it may take a long time to accurately position the ROV for inspection or repair.
ROVs are typically used in determining cracks and fractures inside environments, such nuclear reactor boilers. Several problems arise using ROVs and nuclear reactor boilers. One problem is that irregularities need to be monitored over a period of time (on the order of years) to determine the rate of deterioration. Presently this is accomplished by moving an ROV to a particular position and videotaping the structure or device which is to be examined. At a later date the ROV is positioned at the same site and current data (such as a video image) is compared to previous data. Since it is very difficult to position the ROV at exactly the same site and orientation in three dimensions and obtain a video image from exactly the same viewpoint as previous times, it is difficult to determine differences between images. This tends to be a very subjective determination being made by the operator. The actual cost of maintenance of a nuclear power facility is not only related to the cost of inspection, but is also due to the time that the plant is off-line. This typically can be many times the actual cost of maintenance. It is therefore beneficial to complete inspection and repair in a minimum time period.
A related problem that affects the speed and accuracy of the inspection has to do with the difficulty of retrieving all pertinent past data. If an operator is reinspecting a given location in the reactor, he needs all past information that relates to that site. This may consist of still imagery, segments of past videotapes of a site, auxiliary sensor data such as ultrasound and thermal images as well as non-image data such as written reports and observations or perhaps audio tape recordings of sounds at the site. If this background information is scattered over many physical locations and is recorded or stored on many types of media, (paper, photos, handwritten notes, audio tapes, magnetic video tapes or discs etc) it becomes very difficult to rapidly make inspection decisions.
Another problem which arises in inspecting or examining structures with an ROV is that of planning the actual trajectory of the ROV needed to move it from one site to the next. The environment typically has objects which the ROV must avoid when traveling from one point to another. Currently, an operator examines environment blueprints, and with his knowledge of the ROV size and shape, maneuvers the ROV through the environment. It is very difficult to visualize the full complexity of the 3D environment and whether a given pathway actually will allow passage of the real ROV. Since control of the ROV is complex and demanding, it becomes a very difficult task for the operator to "size up" the suitability of a given approaching pathway while trying to physically control the progress of the ROV.
Currently, there is a need for a system which can provide efficient remote inspection and repair in inaccessible or hazardous environments.